Retrofit Balancing Carbon, Cost, and Social Equity

The urgent push towards net-zero buildings demands more than technical fixes — it requires strategies that balance carbon reductions, cost-effectiveness, and social equity. Retrofitting offers one of the fastest pathways to reduce emissions in existing stock, yet it is also one of the most complex to deliver. From the capital cost of deep retrofits to the equitable targeting of fuel-poor households, the choices we make today will shape the sustainability, affordability, and inclusivity of our future building stock. 

The 2025 CIBSE Technical Symposium brought together cutting-edge research exploring the financial, environmental, and social implications of retrofitting. This blog distils key findings from five technical papers ranging from performance-guaranteed financing models to insulation strategies and HVAC optimisation as well as connecting them to VEXO’s proven energy-saving solutions. 

Empowering Our Homes: The Imperative for Energy Performance Contracting (EPCs) in Residential Buildings 

Lala Rukh et al., University of Galway

Energy Performance Contracting (EPC) offers a financing mechanism where an Energy Service Company (ESCO) implements retrofit measures and is repaid through the guaranteed savings they achieve. Traditionally used in public and large commercial sectors, EPC adoption in residential buildings has been limited—largely due to misconceptions around high upfront costs and complex contracting.

The paper uses a SWOT analysis to highlight EPC strengths, such as policy alignment with Ireland’s National Retrofit Plan, guaranteed savings models, and risk-sharing. Challenges include lack of standardised contracts for small properties, low homeowner awareness, and financing structures not yet tailored for residential scale. Notably, EPCs have demonstrated energy savings of up to 60% in case studies, with the potential to unlock Ireland’s target of 500,000 retrofits by 2030. 

Key takeaways: 
  • EPCs remove upfront capital barriers by financing works from future savings.
  • Policy frameworks increasingly support guaranteed-performance models.
  • Misconceptions about cost remain a key adoption barrier.
  • Small-building EPC models require standardisation to scale.
  • Could be a catalyst for both emissions reductions and social benefits.

How we can help: EPCs thrive on predictable, measurable savings. VEXO S-BMS (Smart Building Management Systems) and VEXO X-POT side-stream filtration improve HVAC system efficiency and longevity, supporting the guaranteed performance that underpins EPC contracts. VEXO clients have been able to achieve energy savings with limited CapEx to meet EPC requirement deadlines such as the deadline for commercial buildings to achieve a minimum EPC rating of C is April 1, 2027. 

A Spatio-Temporal Analysis and Modelling of Fuel Poverty Alleviation Measures in Disadvantaged English Communities 

Audrey Mamelle et al., UCL

Fuel poverty, defined under the UK’s Low Income Low Energy Efficiency (LILEE) metric, remains persistent in certain communities despite policy interventions. This study uses open-source urban building energy modelling to simulate retrofit scenarios for England’s most fuel-poor neighbourhood  — Birmingham 096I, with a fuel poverty rate of 71%. 

Solid wall insulation emerged as the most effective measure in lifting households from fuel poverty, followed by loft and cavity wall insulation. However, high installation costs make solid wall retrofits challenging for large-scale roll-out. Cavity wall and loft insulation were found to be the most cost-effective, balancing capital costs with fuel poverty alleviation potential. 

Key takeaways: 
  • Fuel poverty persists spatially over decades despite national policy targets. 
  • Solid wall insulation offers highest heating demand reduction, but at high cost. 
  • Cavity wall and loft insulation are the most cost-effective solutions. 
  • Urban building energy modelling can improve targeting of retrofit interventions. 
  • Policy schemes need to better match measures to specific community needs. 

Deep Retrofitting: Carbon vs Cost Payback 

Emmanouil Perisoglou et al., Cardiff University 

This study develops a methodology to compare carbon payback and cost payback for deep retrofits, incorporating both operational and embodied impacts. Applied to six off-gas social housing bungalows, the research found that carbon payback (5.9–7.9 years) was nearly eight times faster than cost payback — largely due to the high capital costs of low-carbon technologies versus their significant carbon savings.

Key drivers included embodied carbon from imported PV panels and major operational carbon savings from replacing fossil fuel boilers with heat pumps. The analysis also highlighted the sensitivity of cost payback to future energy price and grid carbon intensity scenarios. 

Key takeaways: 
  • Carbon payback is significantly faster than cost payback in deep retrofits. 
  • Embodied carbon from certain technologies (e.g., PV) is a major consideration. 
  • Fossil fuel replacement delivers the largest operational carbon savings. 
  • Energy price and grid decarbonisation trajectories heavily influence payback. 
  • Holistic metrics are essential to balance climate targets with economic feasibility. 

By optimising heat distribution and reducing system inefficiencies, VEXO’s X-POT shorten operational payback periods, increasing the attractiveness of deep retrofit packages. 

Comparison of Energy Saving for Internal or External Retrofit Wall Insulation in Dwellings 

Richard Lamb, Independent Researcher 

Through finite element thermal modelling of single rooms, this study challenges the assumption that only very low U-values deliver high energy savings. For SAP heating demand patterns, internal insulation with a U-value around 0.6 W/m²K can achieve comparable savings to external insulation at 0.3 W/m²K  —due to faster heat-up times and reduced heating periods. 

The findings are particularly relevant for retrofits where external insulation is impractical or cost-prohibitive. The research stresses the importance of factoring thermal mass and heat storage effects into energy-saving assessments. 

Key takeaways: 
  • Internal insulation can rival external insulation performance for intermittent heating. 
  • Faster room heat-up reduces energy demand despite higher U-value. 
  • Thermal mass effects must be considered in retrofit modelling. 
  • Supports more flexible, context-driven insulation specifications. 
  • Could reduce costs and disruption in heritage or space-constrained properties. 

For retrofits prioritising intermittent heating efficiency, VEXO’s S-BMS enables fine control of heating schedules and zone temperatures, complementing the fast-response nature of internal insulation strategies. 

Potential Energy Saving with High-ΔT Chilled Water Designs Compared to Conventional Low-ΔT Design for Office Buildings in Hot and Humid Climates 

Akila Joseph & Anusha Wijewardane, University of Moratuwa 

Analysing a 26-floor Colombo office building, this study compares chilled water systems with ΔT values of 5°C (conventional), 7°C, and 8.3°C (ASHRAE 90.1 recommended). High-ΔT systems reduce chilled water flow rates, lowering pump energy use by up to 39.8% and enabling smaller pipework. However, air-side equipment increases slightly in size and fan energy use.

Overall chiller plant room energy savings reached 5.1% for the 8.3°C ΔT configuration. The authors recommend high-ΔT designs for climates where water-side energy savings outweigh air-side penalties, supported by accurate load modelling. 

Key takeaways: 
  • Increasing chilled water ΔT reduces pump energy use significantly. 
  • Plant room energy savings of 3.7–5.1% are achievable. 
  • Slight increases in air-side equipment size and fan energy must be managed. 
  • Capital cost savings possible via smaller pipework and reduced plant space. 
  • Best suited for climates with high cooling demand and long operating hours. 

High-ΔT systems demand pristine water quality for consistent heat transfer. VEXO’s X-POT filtration ensures stable ΔT performance by preventing fouling and maintaining coil and pipework efficiency. 

How VEXO Helps 

Across these diverse studies, one theme is clear: successful retrofits require both building fabric improvements and high-efficiency mechanical systems. VEXO’s solutions integrate seamlessly with retrofit strategies: 

  • X-POT – Side-stream filtration and dosing to optimise HVAC hydronic system performance, improving ΔT stability and reducing energy waste. 
  • S-BMS – Smart building management system enabling fine-grained control over heating and cooling schedules for maximum operational efficiency. 
  • Proven customer results include up to 36% reduction in heating energy use, directly enhancing retrofit ROI. 

Whether you are considering deep carbon-cutting retrofits, tackling fuel poverty, or optimising system performance, VEXO’s solutions can help turn performance models into measurable results. 

Get in touch today to discuss your design requirements or book a live demo. 

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References: 

  • Lala Rukh et al. (2025) Empowering Our Homes: The Imperative for Energy Performance Contracting (EPCs) in Residential Buildings. University of Galway. 
  • Audrey Mamelle et al. (2025) A Spatio-Temporal Analysis and Modelling of Fuel Poverty Alleviation Measures in Disadvantaged English Communities. UCL. 
  • Emmanouil Perisoglou et al. (2025) Deep Retrofitting: Carbon vs Cost Payback. Cardiff University. 
  • Richard Lamb (2025) Comparison of Energy Saving for Internal or External Retrofit Wall Insulation in Dwellings. 
  • Akila Joseph & Anusha Wijewardane (2025) Potential Energy Saving with High-ΔT Chilled Water Designs Compared to Conventional Low-ΔT Design. University of Moratuwa. 

To access and download all the papers from the 2025 CIBSE IBPSA-England Technical Symposium head over to: https://www.cibse.org/knowledge-research/knowledge-resources/technical-symposium-papers/2025-technical-symposium-papers/ 

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